feat: add settings import/export functionality

[coderGtm]

What?

Closes #191

This PR implements the ability to export and import non-sensitive AI configuration settings and introduces a dedicated AI section in WordPress Site Health.

Why?

Allowing users to move AI configurations between environments (e.g., staging to production, multi-site etc.) improves the developer experience. By excluding sensitive credentials from the export, we ensure security while maintaining portability. The Site Health integration provides administrators with a quick overview of the plugin's status and credential health.

How?

• REST API: Created includes/REST/Settings_IO_Controller.php to handle GET /ai/v1/settings/export and POST /ai/v1/settings/import.
• Security: Implemented SENSITIVE_PATTERNS filtering to ensure API keys, tokens, and secrets are never exported or overwritten during import.
• Site Health: Added includes/Admin/Site_Health.php to provide debug information (version, enabled features, credential status) and a status test for connectivity.
• UI/UX:
  • Added "Export settings" and "Import settings" to the AI settings menu in routes/ai-home/stage.tsx.
  • Implemented a confirmation modal for imports.
• Tests: Added comprehensive integration tests in tests/Integration/Includes/REST/Settings_IO_ControllerTest.php and tests/Integration/Includes/Admin/Site_HealthTest.php.

Use of AI Tools

AI assistance: Yes
Tool(s): GitHub Copilot
Model(s): Claude Sonnet 4.6, GPT-4o
Used for: Authoring the codebase exploration, UI components, and the integration test suite.

Testing Instructions

1. Navigate to AI Settings.
2. Open the kebab menu (three vertical dots) in the top right.
3. Click Export settings. A JSON file containing your current toggles and developer configurations (but no API keys) should download.
4. Toggle several features to different states.
5. Click Import settings in the menu and select the previously downloaded file.
6. Confirm the prompt "This will overwrite existing AI settings."
7. Verification: The UI should update immediately to reflect the imported settings without a page refresh.
8. Navigate to Tools > Site Health.
9. In the Status tab, verify the "AI Plugin" test results.
10. In the Info tab, verify the "AI Plugin" section contains correct metadata about your setup.

Screenshots or screencast

Menu Items:

Confirmation prompt before completing import:

Changelog Entry

Added - Import/Export functionality for non-sensitive AI settings.
Added - AI-specific Site Health integration and status tests.

[github-actions]

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Co-authored-by: coderGtm <gautam23@git.wordpress.org>
Co-authored-by: dkotter <dkotter@git.wordpress.org>
Co-authored-by: jeffpaul <jeffpaul@git.wordpress.org>

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[coderGtm]

The failing JavaScript quality check is due to a conflict between eslint and typescript. While eslint prefers dot notation, typescript complains about it (TS4111). Should I suppress the eslint error?

[dkotter]

The failing JavaScript quality check is due to a conflict between eslint and typescript. While eslint prefers dot notation, typescript complains about it (TS4111). Should I suppress the eslint error?

We do have a number of these that we already ignore with inline statements so I think that's fine